One known technology to prevent drop accidents due to loosened or detached screws in this type of conventional ceiling fans is to sound an alarm when an attached screw becomes loose. For example, this is disclosed in Japanese Patent No. 3032325.
This ceiling fan is described below with reference to FIG. 17. As shown in the drawing, pipe 101 passing through the center of ceiling fan is suspended from bracket 103 via semi-spherical flange 102. Bracket 103 is attached to mounting plate 105 by attaching screw 106. This mounting plate 105 is attached to a ceiling face by wood screw 104. Microswitch 107 is provided on bracket 103, and actuator 108 of microswitch 107 makes contact with the ceiling face.
To increase the safety, an alarming device is activated via microswitch 107 when wood screw 104 fixing mounting plate 105 or attaching screw 106 fixing bracket 103 is loosened in the conventional ceiling fan. However, if the shaft provided on the motor and the pipe suspending from the ceiling are connected by a connecting bolt via a through hole in this ceiling fan structure, the through hole for the connecting bolt may wear over time and the hole may broaden.
Japanese Utility Model Unexamined Publication No. S56-41115 discloses the next technology for a structure of an externally-rotating motor. A tubular portion is formed in the center of an upper case where an external rotor of the externally-rotating motor is embedded, and an upper ball bearing is press-fitted into this tubular portion. A vertical central shaft of an internal stator is inserted through this upper ball bearing, and a lower ball bearing, already press-fitted to the vertical central shaft, is inserted into the tubular portion in the center. A collar is provided between inner rings or outer rings of the upper and lower ball bearings, and a coil spring is provided between the other rings. The upper ball bearing is fixed to the tubular portion with an interference fit, and the lower ball bearing is fixed to the vertical central shaft with a clearance fit after the lower ball bearing is loosely fitted in the collar.
In this conventional motor, the outer ring of the upper ball bearing is fixed inside the tubular portion, which is a bearing housing, with the interference fit; and its inner ring is connected to the vertical central shaft with the clearance fit. The outer ring of the lower ball bearing is connected to the tubular portion with the clearance fit, and its inner ring and the vertical central shaft are connected with the interference fit. Accordingly, the weight of the rotor is applied in a direction that presses the outer ring of the upper ball bearing downward from a top end of the tubular portion. As deformation or deterioration of the coil spring advance in line with operations, a certain level of appropriate preload cannot be given to the upper and lower ball bearings, although an elastic member such as a coil spring is inserted between the upper and lower ball bearings. This causes distortion in a sliding face inside the upper and lower ball bearings at an early stage, resulting in the generation of a sliding noise. Reduction of this sliding noise has thus been demanded.